As a disk device, a magnetic disk drive comprises a housing including a base and a top cover, and the housing accommodates therein a rotatable magnetic disk, an actuator supporting a magnetic head and the like. As a technique of improving the performance of the disk drive, a method of reducing rotational resistances of the magnetic disk and the magnetic head, by sealing low-density gas in the housing, has been proposed.
In such a magnetic disk drive, the top cover is jointed to the base of the housing by welding to form an enclosed housing and increase the airtightness of the housing. The welding is carried out on along an entire outer circumference of the top cover. Here, in order to obtain high airtightness, it is necessary to maintain a stable welding quality all around the circumference. On the other hand, in the case where the outer diameter of the magnetic disk, the wall portion of the base needs to be formed thinner, which may accordingly decrease the area of the welded portion and degrade the welding quality.